When a Jewish woman intermarries, there are less chances (50%?) the children will identify as Jews. Hence within a few short generations (2-3), there are no more witnesses to their Jewish status. So they lose their halachic status as Jews. Only when Moshiach comes, perhaps their status will be revealed. There may very well be millions of such people roaming the earth now. We have no idea, and they don't make up our current Jewish nation today.
So is that a threat to Jews or just Judaism, if their halachically not counted anymore?